Aluminum alloy



Patented Feb. 9, 1926.

UNITED STATES PATENT OFFICE.

RODERICK L. JOHNSTON, NEW YORK, N. 'Y., RCBERT S. ARCHER, OF EAST CLEVE-LAND, AND ZAY JEFFRIES, F CLEVELAND HEIGHTS, OHIO, ASSIGNORS TO ALUMINUMCOMPANY OF AMERICA, OF PITTSBURGH, PENNSYLVANIA A. COR- PORATION OFPENNSYLVANIA.

ALUMINUM ALLOY.

No Drawing.

T 0 all whom it may concern: 7

Be it known that we, RODERICK L. J OHN- STON, ROBERT S. ARCHER, and ZAYJnrrnms, all citizens of the United States, the said Johnston residingat New York, Kings County, State of New York, and the remaining two atEast Cleveland and Cleveland Heights, respectively, in the county ofCuyahoga and State of Ohio, have invented 10 certain new and usefulImprovements in Aluminum Alloys, of which the following is a full,clear, and exact description.

The presence of small amounts of silicon in aluminum and in aluminumalloys is usually considered objectionable. In the course of aninvestigation upon the effects of silicon we have discovered that byusing a substantial amount of silicon, materially greater than thequantity usually found as 'an impurity, with the addition of a metal ormetals, for example one or more of those hereinafter named, it'ispossible to produce an alloy having excellent casting qualities combinedwith good physical properties.

Among the metals capable of forming solid solutions in the aluminum wehave found copper and zinc particularly advantageous. The metalsreferred to may be used singly or in combination In the use of copperalone, the silicon content of the alloy should in general be not lessthan about 3 per cent nor more than about 10 per cent, and the coppershould be preferably from about 2 per cent to. about 5 per cent; theproportions of copper and silicon being variable, however, according tothe particular combination of properties desired. In general, theattainment of good casting qualities depends largely upon the relativeproportions of the silicon and copper, the latter being preferablyreduced as the former is increased, and vice versa. Increasing thecopper, at least up to the limit of its capacity for entering into solidsolution in the aluminum, tends in general to increase the tensilestrength, especially if subjected to a suitable heat treatment, say thatdescribed in the copending application r of Zay J eifries and Robert S.Archer, Serial No. 435,024. A test bar cast in sand in the ordinary way,of an-aluminum alloy con- Applieation filed November 27, 1920. SerialNo. 426,793.

taining 10 per cent silicon and 3 per cent copper, showed a tensilestrength of about 23,000 pounds per square inch and an elongation ofabout 1.5 per cent in two inches.

Such a bar, after heat treatment by the method described in the abovementioned application, showed an increase of tensile strength up to30,000 pounds per square inch and an increase of elongation up to 2.5per cent. A bar of the same alloy but cast in a chill mold, in order tocause rapid solidification of the molten metal, was found to have atensile strength of about 30,000 pounds per square inch and anelongation of about 2.7 per cent, even without heat treatment. A similarbar, heat treated, had a tensile strength of 40,000 pounds per squareinch and 6 per cent elongation. On the other hand, a chill-castheat-treated bar of an alloy containing about 6 per cent silicon andabout 4 per cent copper was found to have a tensile strength exceeding42,000 pounds per square inch and an elongation exceeding 8 per cent in2 inches.

The addition of zinc up to about 5 per cent has a slight effect on thetensile strength of the alloy. Above that amount a greater increase oftensile strength is observed. The presence of the zinc is often anadvantage by reason of the whiter color of the polished alloy. We havefound that with the addition of an alkali metal or metals to the alloy,as described in the copending application of Junius D. Edwards, Francis(J. Frary and Harry V. Churchill, Serial No. 426,796, now Patent No.1,410,461, issued March 21, 1922, very satisfactory physical propertiescan be obtained alongwith the other advantages incident to the presenceof the zinc, particularly if the alloy to which alkali metal has beenadded is cast in such a manner, as for example by the use of a chillmold, that the molten metal is caused to solidify rapidly. For instance,an alloy containing about 10 per cent zinc and about 8 per cent silicon,to which alkali metal had been added and which was cast in a chill mold,has been found to have a tensile strength exceeding 42,000 pounds persquare inch, with an elongation up to 7 per cent in two inches. Asimilar casting, after being subjected to In the case ofaluminum-silicon alloys containing both copper and zinc, a sand casttest bar of an alloy containing 8 per cent silicon,*10 per cent zinc and2.5 per cent copper, was found to have a tensile strength of 27,000pounds per square inch and an elongation of 1.5 per cent. This alloy isalso susceptible to improvement by addition of alkali metal beforecasting; sand cast specimens-of the alloy so treated having a tensilestrength of 30,000 pounds per square inch with an elongation of 2 percent, while chill'cast specimens have a tensile strength of 38,000pounds per square inch and an elongation of 3.5 percent. Heat treatmentby the method described in the application of Archer and Jeflriesbefore-referred to has been found to increase the tensile strength ofthe chill cast alloy up to 45,000 pounds per square inch and at the sametime increase the elongation to 7.5 per cent.

In the alloys referred to above we have observed that the elongation isbetter if the iron content is low, and for that reason there are manycases where the iron should not exceed about 0.6 per cent. In othercases much higher iron can be used, especially in chill castings, as forexample pressure die castings.

The alloys described herein are also well adapted to forging and likeoperations.

We claim:

1. An-alloy composed chiefly of aluminum, containing a substantialamount of silicon and substantial amounts of copper and zinc.

2. An alloy composed chiefly of aluminum,

containing a substantial amount of silicon,

copper not exceeding about 5 per cent, and a substantial amount of zinc.

3. An alloy composed chiefly of aluminum, containing a substantialamount of silicon,

containing silicon in substantial amount but not exceeding about 10 percent, and substantial amounts of copper and zinc.

6. An alloy composed chiefly of aluminum, containing between 3 and 10per cent silicon, approximately, and substantial amounts of copper andzinc.

7 An alloy composed chiefly of aluminum, containing between 3 and 10 percent silicon, approximately, copper between 2 and 5 per cent,approximately, and asubstantial amount of zinc.

8. An alloy composed chiefly of aluminum, containing between 3 andlO percent silicon, approximately, a substantial amount of copper, and zincbetween 5' and'15 per cent, approximately.

9. An alloy composed chiefly of aluminum and low in iron, containingcopper between 2 and 5 per cent, and silicon between 3 and 10 per cent,approximately.

10. An alloy composed chiefly of aluminum. and low in iron, containing 4percent copper and 6 per cent silicon, approximately.

11. An alloy composed chiefly of aluminum, containing a substantialamount of silicon and substantial amounts of copper and zinc, with aniron content not exceeding about 0.6 per cent.

12. An alloy composed chiefly. of aluminum, containing copper between 2and 5 per cent, and silicon between 3 and 10 per cent, approximately,with an iron content not exceeding about 0.6 per cent.

-In testimony whereof we hereto afiix our signatures.

RODERICK L. JOHNSTON. ROBERT S. ARCHER. ZAY .JEFFRIES.

